1. Field of the Invention
The present invention relates to an inserter which is connected to an image forming apparatus, for supplying an insert-sheet.
2. Description of the Related Art
Conventionally, in the image forming apparatuses such as copying machines, some are provided with function modes such as a cover mode and an interleaving sheet mode for inserting a cover or an interleaving sheet to a plurality of sheets having images formed thereon, to thereby perform book binding or the like.
Those modes are provided for inserting, as a cover, an interleaving sheet, or a back cover, a sheet for insertion (hereinafter, referred to as “insert-sheet”) which is different from the sheet having an image formed thereon, to a first page, last page, or middle page of the plurality of sheets having images formed thereon. This inserting operation is carried out on a tray on which the sheets having images formed thereon are to be stacked, for forming a sheet set (bundle) in which the insert-sheets are inserted to predetermined positions of the plurality of sheets having images formed thereon.
In the cover mode and the interleaving sheet mode described above, arbitrary settings may be made about a sheet insertion position (at what page) or a number of insertions of sheets to be inserted with respect to the sheet-bundle to be formed.
Further, with respect to the sheet set, to which the insert-sheet is inserted, processing per bundle, namely, post processing such as bundle discharge processing, stapling processing, folding processing, or book binding may be made in a post processing apparatus (sheet processing apparatus) such as a finisher installed in the image forming apparatus.
Hereinafter, operation modes for inserting, as the cover, the interleaving sheet, and the back cover, the insert-sheet fed from the insert-sheet container unit are generally called an sheet insertion mode.
As a method (mechanism) of supplying the insert-sheet, there is given a method involving supplying the insert-sheet using one of a plurality of sheet feeder cassettes provided to the image forming apparatus. In this method, if timing for inserting the insert-sheet comes, the sheet feeder cassette in which the insert sheet is stored is selected, and the insert-sheet is fed to a conveying path as well as recording sheets for image formation.
Then, the fed insert-sheet is laid on the recording sheets having images formed thereon on the tray of the sheet processing apparatus. With this operation, there is produced a sheet set in which the insert-sheet is incorporated.
In a midway of the above-mentioned path, for example, in an image forming apparatus using an electrophotographic system, there is arranged a fixing unit for fixing toner images for forming the images on the sheets, and hence the insert-sheet passes through the fixing unit, resulting in being heat-pressed as well as the sheets on which images are formed.
In this case, if a color image print script is used as the insert-sheet, quality of the printing image may be impaired by being heat-pressed when the insert-sheet passes through the fixing unit.
Further, in recent years, as color images are increasingly used with spreads of personal computers, color copy paper and color print paper are used in many cases as the insert-sheets. For that reason, there occurs a problem in that quality of bookbinding or the like, which is subjected to bundling processing, lowers owing to deterioration of the insert-sheet.
Therefore, there has been seen an image forming system having a structure in which the inserter for supplying the insert-sheet is provided to the post processing device such as a finisher, which is installed to the image forming apparatus, to thereby supply the insert-sheet without causing to pass through the image forming apparatus (for example, refer to Japanese Patent Application Laid-Open No. 2003-221160).
In addition, due to recent rapid expansion of print on demand (POD) market, in a system which is built around the image forming apparatus of electrophotographic system, for carrying out the image formation in large quantity, there has been attempted employment of multistage sheet feeder cassettes, or capacity increase of the cassette in a sheet feeding apparatus. In this case, to the inserter, various and large amounts of preprint paper, a plurality of color paper, tab paper, or the like may be stored (for example, refer to Japanese Patent Application Laid-Open No. 2004-051268).
Further, the image forming apparatus of the electrophotographic system generally discharge the sheet to the downstream side device such as the inserter or the finisher under any one of the following states: a state in which an image formation surface faces downward (face-down); a state in which the image formation surface faces upward (face-up); and a state in which the image formation surfaces are both surfaces.
For that reason, when discharging the sheet in the face-down state, a front surface and a rear surface of the sheet are inverted by switch back. However, in order to prevent the next sheet from being fed during the switch back of the sheet, it is necessary for intervals of the sheets to widen. To cope with this, the sheet is discharged to the downstream side device at higher speed compared to the face-up discharge with no switch back (for example, refer to Japanese Patent Application Laid-Open No. 2005-089009).
However, in the conventional inserter, the insert-sheet is passed-over at constant speed to the downstream side device. In this case, conveying speed of the insert-sheet has no relation with changes in speeds of the sheets before and after the insert-sheet, which are conveyed from the image forming apparatus.
Further, the finisher switches over speeds of conveying rollers to receive the sheet to be conveyed at a speed selected from a plurality of speeds from the image forming apparatus and the sheet to be supplied at the constant speed from the inserter.
For that reason, in a job in which the inserter is used, the finisher is required to change the speeds of the conveying rollers for increased times, and hence the sheet interval is widened in order to gain time which is necessary for switching over the roller speed. As a result, productivity required for POD is significantly lowered.